“Drop-in” hot runner systems are those having nozzles that are connected to the manifold so that that the system can be installed into a mold as an assembled unit. Drop-in systems often have “screw-in” nozzles which are attached to the manifold by a threaded connection therebetween. Since the nozzles are secured to the manifold, thermal expansion of the manifold causes the position of each nozzle to be different when the hot runner is heated compared to when the hot runner system is unheated, (e.g. when the system is in a cold condition). However, when the hot runner system is installed in a mold, the downstream end of the nozzle is held in position relative to the mold, and thermal expansion of the manifold creates a side load on the nozzle.
In some instances the length of the nozzle is long enough to accommodate thermal expansion side loading by flexing or bending without also compromising the hot runner system and/or the mold. However, if the length of the nozzle is too short, or thermal expansion of the manifold is too great, side loading of the nozzle may compromise the hot runner system and/or the mold. Such instances require a nozzle that is coupled to the manifold to facilitate handling of the hot runner system as a unitary assembly, but is not subjected to excessive side loads when the manifold is heated.
“Flange” or compression seal nozzles have been loosely bolted to the manifold to facilitate handling the hot runner system as a unitary assembly. As the hot runner system is installed into the mold, the nozzle flange engages with a lead-in of a flange locating bore in a mold plate which causes the nozzle to slide relative to the manifold and find its precise cold condition location. This solution increases the difficulty in installing the hot runner system as the number of nozzles increases. Furthermore, the amount of “play” between the nozzle and the manifold required to allow each nozzle to find its position increases the likelihood of a hot runner component, such as nozzle tip, being damaged as the hot runner system is installed into the mold.
Flange nozzles have also been bolted to the manifold at their cold condition location by using dowels that extend through manifold and into the nozzle. To permit thermal expansion of the manifold, the dowels are removed from the nozzles prior to heating the manifold otherwise force created by thermal expansion of the manifold may damage the nozzle and/or the manifold. Also, this solution is only practical in applications where there is access to the dowels when the system is assembled, for example, with nozzles that do not have a valve actuator that is in line with the nozzle.